The effective mixing of two or more fluid components, particularly where one or more of such fluids is relatively highly viscous and reactive, is sometimes difficult to accomplish. For production line operation, as in a molding process, a product mix of suitable quality must be produced at a reasonably fast rate so that the ultimate molded unit can be fabricated at an economically profitable rate. For example, in the mixing of some viscous materials, which react chemically to form a polymer such as polyurethane, the mixing apparatus for use in a molding process, often must be arranged to supply a discrete quantity of a product mix on a discontinuous, or batch, basis, the quality of the mix being required to be sufficiently high that the quality of the molded product is not deleteriously affected.
Moreover, the mixing rate must be high enough so as to provide a good quality of mixing before the reactive fluid compounds undergo a significant amount of reaction in the mixing chamber. It is essential that the mixed liquid remain at a sufficiently low viscosity until the mold is completely filled. Since the ultimately desired physical properties of the mixed material, such as its low-temperature, flexibility and modulus characteristics, depend on the molecular weights of the reacting liquids and thus, on their viscosities, an effective mixing apparatus should not be limited by the viscosity characteristics of the liquid components being mixed.
Further, any production system must be such that the desired production rate should be achieved at a reasonable cost, the size and complexity of the device being such that installation and maintenance expenses can be held to reasonable levels.
A common problem with many continuous and certain batch mixers is that they must be periodically cleaned to prevent an over-accumulation of reacted material from adversely affecting the performance of the apparatus. Often, because of the complicated geometry of the mixer, the cleaning operation must be laboriously performed by hand, the overall costs thereby increasing due both to the additional labor required and to the decreased oproduction which results because of machine down time.